Along with continued evolution of a wireless communication technology and standard, mobile packet services are greatly developed, and data throughput of single User Equipment (UE) is continuously improved. For example, a Long Term Evolution (LTE) system may support downlink data transmission at a maximum rate of 100 Mbps within a 20M bandwidth, and a data transmission rate of a subsequent LTE advanced system may further be increased, and may even reach 1 Gbps.
Explosive growth of data services of UE gradually tensions existing network resources particularly under the condition that network layout of a new-generation communication technology (such as 3rd-Generation (3G) and LTE) may not be widely implemented, which consequently causes incapability in meeting requirements of users on rate and traffic and poorer user experiences. How to prevent and change such a condition is a problem that an operating company must consider, and on one hand, it is necessary to accelerate popularization and network deployment of a new technology; and on the other hand, it is expected that an existing network and technology may be enhanced to fulfil the aim of rapidly improving network performance. As everyone knows, except a wireless network technology provided by the 3rd Generation Partnership Project (3GPP), a Wireless Local Area Network (WLAN) which has been widely applied at present, particularly an IEEE802.11-standard-based WLAN, has been widely applied to hotspot access coverage in homes, enterprises and even the Internet, wherein a technical specification proposed by the Wireless Fidelity (WIFI) Alliance is most widely applied, so that a WIFI network usually equals to the IEEE802.11-standard-based WLAN in practice, and under the condition of no confusions, a WIFI module is adopted to describe wireless transceiver and processing modules supporting WLAN in a network node hereinafter.
On such a premise, some operating companies and enterprises have proposed to merge a WLAN and an existing 3GPP access network to implement joint transmission and fulfil the aims of offloading the existing 3GPP access network and improving network performance by virtue of the WLAN. The 3GPP has formulated a related protocol for interworking between the 3GPP access network and the WLAN at present. As shown in FIG. 1, an interworking WLAN architecture of the 3GPP allows the WLAN to use an Authentication Authorization Accounting (AAA) server in the 3GPP access network for unified authentication and authorization, a packet data network gateway in the existing 3GPP access network may also be multiplexed as a packet data gateway of the WLAN, and in addition, unified accounting, charging and the like of the two networks may also be implemented to achieve loose coupling of the two networks.
However, a current interworking architecture also has some shortcomings, and for example, current interworking is triggered by UE, a 3GPP network side may not control a target access network, and although a network element Access Network Discovery Support Function (ANDSF) of a core network side may give some strategic rules, these rules are relatively static and the 3GPP network side loses control over access network selection of the UE, which may cause the problem that an access network selected by the UE may not meet a requirement of the UE on Quality of Service (QoS), or may cause frequent handover of the UE between the 3GPP access network and the WLAN to influence user experiences and simultaneously increase an unnecessary network load.
Therefore, it is necessary for the 3GPP access network to participate in network selection of the UE to control handover or offloading of the UE between the 3GPP access network and the WLAN partially or completely at present.
A conventional art has a problem as follows: in a scenario of a cell handover process of a terminal, when a WLAN is located in a range of a handover area of the terminal, as shown in FIG. 2, coverage of two 3GPP cells which are Cell 1 and Cell 2 is overlapped, the overlapped part is called the handover area, there is also a WLAN called WLAN 1 deployed by an operating company in this range, and then WLAN offloading in the handover process is likely to occur. However, offloading at this time may be unstable. For example, if the UE is being handed over from Cell 1 to Cell 2, the UE simultaneously offloads part of or all services to the WLAN according to a threshold or strategy provided by Cell 1, but Cell 2 may not support a function of handover or offloading between a 3GPP access network and the WLAN or Cell 2 supporting the function has a threshold or strategy different from that of Cell 1, an offloading preparation made by the UE may not work after the UE is successfully handed over to Cell 2 if the UE continues making the offloading preparation according to the threshold or strategy provided by Cell 1, which may cause waste of energy of the UE as well as resource waste.